Method for making concrete articles



Patented Mar. 14, 1950 METHOD FOR MAKING CONCRETE ARTICLES f William S. Ramsay, Canton, Ohio, assignor to The Stark Brick Com poration oi' Ohio pany, Canton, Ohio, a cor- .iipplication March 18, i948, Serial No. 15,604

(Cl. 25-l54) Claims. i

The invention relates to a method of forming molded concrete articles such as blocks, slabs, lintels, window sills and the like, and more particularly to a method of iormingsuch articles from a concrete mixture o a consistency which may be poured into the molds, and rapidly hardening the molded articles.

An object of the invention is to provide a method or forming molded concrete articles which consists in pouring a concrete mixture into a mold and then passing an electric current back and forth through the molded concrete article in opposite directions.

Another object is to provide for the manufacture of molded concrete articles by pouring a concrete mixture into a mold, two opposite walls ci which are electric conductors to which op-a posite sides of an alternating current circuit are connected.

A still further object is to provide a method of making 'molded concrete articles which consists in mixing cement and aggregate with sumcient water so that the mixture may be poured, adding an electrolyte to the mixture and pouring it into a mold and passing an electric current back and forth through the molded article in opposite directions.

Another object of the invention is to provide a method of making such articles which consists in pouring a concrete mixture into a mold and passing an electric current back and forth through the same in opposite directions until the temperature of the concrete is raised to the desired point.

A further object is to provide a method of making molded concrete articles in the manner above referred to, in which the concrete mixture is conned in a mold designed to remove moisture therefrom while the electric current is passed therethrough, whereby excess moisture is caused to escape from the molded concrete article during this operation.

'I'he above objects together with others which will be apparent from the drawing and following description, or which may be later referred to, may be attained by carrying out the improved method in the manner hereinafter described in detail, by means of apparatus illustrated in the accompanying drawing, in which;

Figure l is a vertical, longitudinal sectional view through a mold designed for carrying out the invention, showing a molded concrete article therein, taken as on the line I-I, Fig. 3, and on. a somewhat larger scale than Fig. ,3;

Fig. 2 a vertical, transverse section through the mold, taken as on the line 22, Fig. 3;

Fig. 3 a plan sectional view through the mold, on a smaller scale than Figs. 1 and 2;

Fig. 4 a transverse sectional view through a mold adapted for carrying vout the invention for molding a cored, or hollow, concrete article; and

Fig. 5 a transverse sectional view through another form of cored mold.

Although the method to which the invention pertains is adaptable for molding concrete articles of various shapes, for the purpose of illustration the invention is shown and described as adapted for forming a molded concrete block or slab such as indicated generally at it, which may be used as a window sill, lintel, or the like.

The' article shown is oi considerably greater length than width, and the width is also somewhat greater than the thickness. lt is not intended, however, that the inventionbe limited to the making of an article oi any such relative proportions, as a cube or similar article may be formed by the improved method.

For the purpose of molding the concrete article l0, a mold such as shown in Figs. l, 2 and 3 may be provided, said mold being preferably so constructed that all moisture, in excess of that required to hydrate the cement, will be rapidly eliminated from the concrete mixture.

This mold may comprise the bottom wall I I, the side walls I2 and the end walls Il, which may be vertically grooved, as shown at I4 in Fig. 3, to receive the ends of the side walls so as to properly locate said side and end walls relative to each other.

Two opposite Walls of the mold are electric conductors, being either formed of suitable metal or having their inner surfaces comprising copper or other suitable sheet metal, as indicated at I5 in Figs. 2 and 3, to which are connected opposite sides of an alternating current circuit as indicated at I6.

Where the concrete article to be formed has `one dimension less than the others, the conductors are so arranged that the current passing between the conductors will pass through the article in the shortest path. For this reason, as shown in Figs. 2 and 3 the conductors I 5 are provided upon the inner surfaces of the side walls I2, so that the current will pass through the thickness of the article, which is less than the width or length thereof. l

In carrying out the invention, hydraulic cement and aggregate are mixed in suitable proportions with suiiicient water to form a slurry which may be poured into molds. This concrete mixture or slurry is then' poured into a mold such as shown 3 in Figs. 1, 2 and 3, filling the mold with the concrete mixture as indicated at Ill.

Alternating current; is then passed back and forth through the concrete mixture, between the conductors I5, and in a very short time the molded concrete article is sufilciently hardened so that it may be removed from the mold and handled without danger of injury thereto.

Wlhen using water from some localities, and with some hydraulic cements, which are not good electric conductors, it may be necessary to add a small amount of an electrolyte to the concrete mixture in order that the electric current may be freely passed therethrough.

Calcium chloride makes a very good electrolyte for this purpose, although borax, sodium carbonate and other electrolytes will give satisfactory results. Only a very small amount of electrolyte is required, usually only about 1/m of 1% of the concrete mixture.

In carrying out the improved method the mold is preferably constructed so as to facilitate the escape of moisture from the concrete mixture during the operation. A top wall l1 is preferably provided upon the mold, and tie bolts I0, having nuts I9 thereon. may be provided for holding the ,mold in assembled condition, clamping the side and end walls, i2 and i3 respectively, between the bottom wall Il and top wall I1, as shown in the drawings.

Although the invention may be advantageously carried out in molds constructed in this manner, without any means for removing moisture from the concrete mixture in the mold, it has been found that the efilciency of the method is greatly increased by removing the excess moisture while the alternating current is being passed through the concrete in the mold.

This may be accomplished to a considerable extent by placing gaskets or liners of muslin, canvas, burlap, felt or other non-conducting, absorbent material against the inner surfaces of at least some of the walls of the mold, to absorb excess moisture from the concrete mixture in the mold.

To attain the best results it has been found that substantially all of the excess moisture, above that required to hydrate the cement, may be more quickly removed by perforating at least some of the walls of the mold and placing absorbent gaskets or liners against the inner surfaces thereof.

To this end the top, bottom and end walls of the mold, which are formed of non-conducting material, may be perforated over their entire areas as indicated at in Figs. 1, 2 and 3, and absorbent gaskets or liners 2| may be placed over the inner surfaces thereof, as shown in said dgures of the drawings, to prevent the concrete mixture from entering the apertures 20, while permitting excess moisture to pass freely therethrough.

As an example of the manner in which the invention may be carried out, in one instance one part of Portland cement (calcium silicate) and four parts of aggregate were mixed with sumcient water so that the mixture could be easily poured.

After a mold having opposed conductor walls, as above described but of substantially watertight construction, had been filled with the concrete mixture, a 220 volt, 60 cycle alternating current was passed back and forth through the concrete mixture in the mold, between the conductors l5, and in thirty seconds the temperature of the concrete reached a temperature of about 210 F., and the mold was immediately opened and the molded concrete article removed.

Although no moisture was removed from the concrete mixture it was found that the molded concrete article at this time was suiflciently hardened so that it could be handled without danger of breakage, the article being at that time in the same condition as concrete articles molded under present practice, twenty-four hours after pouring the concrete into the mold.

This is a very great advantage as in ordinary practice of molding concrete articles the concrete mixture is poured into the mold and allowed to remain therein for twenty-four hours. Thus each mold is tied up for twenty-four hours in the molding of a single article and in some cases these molds are quite expensive to produce.

With the present method the article is in condition to be removed from the mold a few seconds after the concrete is poured and the same mold may be used over many times during the twentyfour hour period.

In another instance the invention was practiced upon poured concrete articles, using calcium aluminate cement. In this case one part of calcium aluminate cement was mixed with four parts oi' a burned clay aggregate and suiiicient water so that the mixture could be poured.

This concrete mixture was poured into a substantially water-tight mold as above described with no means for eliminating excess moisture, and alternating eurent passed therethrough for about two minutes, at which time the temperature of the concrete was raised to about 210 F. and the mold was opened and the concrete article removed therefrom.

Within a few minutes from the time one of these articles was removed from the mold, it was subjected to tests and it was found that the molded concrete article withstood a crushing load of 500 pounds per square inch.

In order to illustrate the advantages of passing alternating current through the concrete mixture in the mold, over present practice where the concrete mixture is poured into an open mold in which it is necessary that it stand for twentyfour hours before it may be removed, various tests have been made to show comparisons between present practice and the improved method, with and without perforations and absorbent gaskets in the molds.

For instance, a mixture of one part Portland cement and four parts aggregate was poured into an open mold and allowed to stand twenty-four hours at a room temperature of about 70 F. after which the molded concrete article was sufficiently hardened so that it could be removed from the mold. At the end of forty-eight hours from the time the concrete was poured this article withstood a crushing pressure of pounds per square inch.

The same concrete mixture was poured into a substantially water-tight mold and alternating current passed therethrough for about fifty seconds, raising the temperature to about 210 F. The article was then removed from the mold and in forty-eight hours it withstood a crushing pressure of pounds per square inch.

In another test the same concrete mixture was poured into a mold having absorbent gaskets or liners over the inner surface of some of its walls. and an alternating current was passed therethrough for about sixty seconds, raising the temperature to 220 F. The molded article was then 15 strong enough to be removed from the mold and in forty-eight hours itwithstood a crushing pressure of 138 pounds per square inch.

This shows clearly that the passing of the alternating currentl through the concrete mixture is very advantageous, in that the molded article has sufficient strength that it may be removed from a mold within a minute of the ltime it is poured, instead of after twenty-four hours as in present practice. It also shows that the ultimate strength ofthe article is materially increased by passing the alternating current therethrough.

These tests further show that it is advantageous to remove excess moisture from the concrete mixture while the alternating current is passed therethrough in that the ultimate strength of the article molded in this manner is further increased.

In another series of tests a mixture of one part of calcium aluminate cement and four parts of a burnedclay aggregate, with suillcient water so that the mixture could be poured, was poured into molds and alternating current passed therethrough.

In one instance this concrete mixture was poured into a mold made substantially watertight by the use of a rubber gasket and alternating current was passed through the concrete mixture in the mold for a period of one and onehali to two minutes until the temperature was raised to about 240 F. when the molded concrete article was suiliciently strong that it could be immediately removed from the mold.

One hour after pouring, this article withstood a crushing pressure 'of 225 pounds per square inch, and forty-eight hours after pouring it withstood a crushing pressure of 1620 pounds per square inch.

Using the same mold, but without the rubber gaskets to make it substantially water-tight, the same mixture was raised to a temperature of about 214 F. by passing alternating current therethrough for the same length of time when the article was sufficiently strong to beimmediately removed from the mold. One hour after pouring this article withstood a crushing pressure of 300 pounds per square inch.

Again using the same mold but with absorbent gaskets or liners upon the inner surfaces of some of the mold walls, this same concrete mixture was brought to a temperature of about 240 F. in one and one-half to two minutes, and one hour after pouring the molded article withstood a crushing pressure of 520 pounds per square inch, and forty-eight hours after pouring it withstood a crushing pressure of 1820 pounds per square inch.

In another test the same concrete mixture was -poured into a mold having perforate walls, with absorbent gaskets or liners upon the inner surfaces thereof, as shown in the drawing, and an alternating current passed back and forth therethrough for a period of between one and onehalf and two minutes, at which time the temperature was raised to about 250 F.

The molded concrete article was then sufi-iciently strong so that it could be removed from the moldand handled without danger and one hour after pouring, this article withstood a crushing pressure of 600 pounds per square inch, and 48 hours after pouring'it withstood a crushing pressure of 3200 pounds per square inch.

Another test was made using a concrete mixture nf high, early strength, Portland cement, which was poured into a mold having perforate walls with cloth gaskets or liners therein, and alternating current was passed therethrough for 58 seconds. at which time the molded concrete article was removed from the mold. Twenty-four hours after pouring this article withstood a crushing pressure of 300 pounds per square inch.

This same concrete mixture was poured into an open mold and allowed to set therein for twenty-four hours, as in present practice, and at the end of twenty-four hours the molded concrete article was removed from the mold and withstood a crushing pressure of only 100 pounds per square inch.

The above tests yillustrate clearly that the passing of the alternating current through the concrete mixture in the mold not only reduces the time for hardening the molded article suiciently to remove it from the mold, from twenty-four hours as in present practice, to one or two min- `utes, but alsovshow that the strength of the molded article is considerably increased.

These tests show further that by absorbing `some of the moisture from the concrete mixture, with absorbent gaskets or liners, the strength of the article is considerably further increased, and that by molding the concrete articles in perforate molds, provided with absorbent liners, a much greater strength in the molded article is ati tained.

After molding concrete articles in the manner above described they may be cured in a steam chamber, or by any otherconventional manner such as is common with molded concrete articles which have remained in the mold for twenty-four hours after pouring.

It is believed that the hardening of the molded concrete article is not due entirely to drying action taking place therein but that a chemical action, caused by the passing of the alternating current through the concrete, is at least partially responsible for the rapid hardening of the articles within the molds.

However since the tests show that even better results are obtained by driving off the excess moisture from the concrete mixture by means of the absorbent gaskets or liners and perforate mold walls, as well as by raising the temperature above the boiling point of water, it seems obvious that both the chemical change and drying action combine to produce the desired result of Vhardening the molded article.

For the purpose of illustrating the manner in which a cored concrete article may be made by the improved method, in Fig. 4 is shown a mold designed for producing a cored article, the mold being made in the same manner as the mold shown and described in Figs. 1, 2 and 3 and comprising the perforate bottom wall Ila and side walls I2a having the metal conductors lia upon their inner faces connected to opposite sides of an alternating current circuit as indicated at ISa.

A perforate top wall lla, with absorbent gasket 2la therebeneath, may be clamped upon the top of the mold as by the tie bolts I8a, as above described, and the end walls of the mold (not shown) may be perforated as in Figs. 2 and 3, and absorbent gaskets may be provided therefor as Well as for the perforate bottom wall.

Cores 22, formed of non-conducting material, such as wood, plaster or thelike, may be attached to one side wall by nails orthe like as indicated at 23, so as to form openings of any desired size, shape and location within the moldedconcrete article Illa. ,y

For the purpose of facilitating the removal of moisture from the concrete mixture, the cores 22 may be hollow, as shown, and provided with a,soo,soo

perforations Il, and may be surrounded by abcored article to be molded, it may not be practical or desirable to pass the alternating current back and forth through the molded concrete article in a direction parallel to the cores. Such a case is shown in Fig. 5, in which is illustrated a mold for forming a cored, concrete block, the top and bottom surfaces of which are of irregular contour and vertical cored openings are provided therethrough.

Owing to the irregular shape of the bottom and top walls IIb and Hb respectively of the mold, it is not desirable that these walls have conductors so shaped and attached to their inner surfaces, and it has been found more convenient and practical that the conductors lib are located upon the inner surfaces of the dat side walls l2b, and connected to opposite sides of an A. C. circuit as indicated at IIb.

'I'herefore the bottom and top walls of the mold are preferably formed of non-conducting material and perforated, as shown in Fig. 5, and the inner surfaces thereof lined with absorbent gaskets 2lb as shown. The end walls (not shown) are alsonon-conductors and may be perforated.

TheA cores 22h are located vertically through the mold and may have one end connected to the lower wall of the mold and the other end contacting the upper wall, as shown.

It was found that with such an arrangement of the parts that, where the cores were non-conductors, the concrete adjacent to the cores would not harden properly by passing the alternating current therethrough. However when the cores 22h were covered with conducting material, such as sheet copper indicated at 22o, the molded concrete block was quickly hardened by passing the alternating current back and forth therethrough.

Throughout the specification and claims where aggregate is referred to, it should be understood that any aggregate ordinarily used in the making of concrete structures is adapted for this method, such for instance as blast furnace slag, expanded blast furnace slag, cinders, sand, or Vsand and gravel, calcined fire clay, expanded burned clay or shale, asbestos, expanded vermieulite, pumice,

expanded perlite, and diatomaceous earth.

It has been found that in the manufacture of 'insulation slabs or bricks, expanded vermiculite is a very satisfactory aggregate owing to its light weight. As an example, in the manufacture of structural insulation slabs, one part of Portland cement and seven parts of expanded vermiculite were mixed with sufficient water so that the concrete mixture could be poured into a mold such as illustrated in the drawing and above described.

After passing an alternating current through the mold for about one minute the temperature was raised to about 210 to 212 F. and the molded slab was sufficiently strong that it could be immediately removed from the mold.

In the manufacture of refractory insulation bricks, one part of calcium aluminate cement and seven parts of expanded vermiculite were mixed with suflicient water so that the concrete mixture could be poured into a mold. An alternating current was passed through the mold for about brick was sufficiently strong that it could be immediately removed from the mold.

Expanded vermiculite may also be used as an aggregate for producing a light weight concrete building block, in which case in order to increase the strength of the block the proportion of aggregate may be reduced`to as low as four parts of expanded vermlculite to one part of cement. Either Portland cement or lcalciumaluminate cement may be used with the expanded vermiculite aggregate and the invention is carried out ln the manner above described.

I claim:

1. The method of making molded concrete articles which consists in mixing hydraulic cement and aggregate with suiiicient water to produce a concrete mixture which may be poured, then pouring the mixture into a mold having two opposed walls composed entirely of conducting material and the remaining walls composed of non-conducting material perforated over their entire areas, and passing a 60 cycle alternating current back and forth between the walls of conducting material throughout the entire mass of the concrete mixture, the voltage of said alternating current being sufdcient to raise the temperature of the concrete mass to 210 F. to 250 F. and to drive the moisture out of the concrete mass so that it may be removed from the mold in not over two minutes time.

2. The method of making molded concrete articles which consists in mixing hydraulic cement and aggregate with suilicient water to produce a concrete mixture which may be poured, then pouring the mixture into a mold having two opposed walls composed entirely of conducting material and the remaining Walls composed of non-conducting material perforated over their entire areas, and passing a 220 volt 60 cycle alternating current back and forth between the walls of conducting material throughout the entire mass of the concrete mixture, the voltage of said alternating current being suiiicient to raise the temperature of the concrete mass to 210 F. to 250 F. and to drive the moisture out of the concrete mass so that it may be removed from the mold in not over two minutes time.

3. The method of making molded concrete articles which consists in mixing hydraulic cement and aggregate and a small amount of electrolyte with suilicient water to produce' a concrete mixture which may be poured, then pouring the mixture into a mold having two opposed walls composed entirely of conducting material and the remaining walls composed of non-conducting material perforated over their entire areas, and passing a 60 cycle alternating current back and forth between the walls of conducting material throughout the entire mass of the concrete mixture, the voltageof said alternating current being suiiicient to raise the temperature of the concrete m'ass to 210 F. to 250 F. and to drive the moisture out of the concrete mass so that it may be removed from the mold in not over two minutes time.

4. The method of making molded concrete articles which consists in mixing hydraulic cement and aggregate and a small amount of calcium chloride with sufilcient water toy produce a concrete mixture which may be poured, then pouring the mixture into a mold having two opposed walls composed entirely of conducting material and the remaining walls composed of non-conducting material perforated over their entire areas. and passing a 60 cycle alternating current back and forth between the walls of conducting material throughout the entire mass of the concrete mixture, the voltage of said alternating current being sufficient to raise the temperature of the concrete mass to 210 F. to 250 F. and to drive the moisture out of the concrete mass so that it may be removed from the mold in not over two minutes' time. y

5. The method of making molded concrete articles which consists in mixing hydraulic cement and aggregate with suicient water to produce a concrete mixture which may be poured, then pouring the mixture into a mold having two opposed walls composed entirely of conducting material and the remaining Walls composed of nonconducting material perforated over their entire areas, and passingA a 60 cycle alternating current back and forth between the walls of conducting material throughout the entire mass of the concrete mixture, the voltage of said alternating current being sufficient to raise the temperature of the concrete mass to 210 F. and to drive the moisture out of the concrete mass so that it may be removed from the mold in about one minute.

S. RAMSAY.

REFERENCES ,CITED The following references are of record in thel le of this patent:

UNITED STATES PATENTS Number Rener Aug. 31, 1948 

